constellation-server 1.12.0

Pluggable authoritative DNS server. Entries can be added & removed from an HTTP REST API.
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// Constellation
//
// Pluggable authoritative DNS server
// Copyright: 2018, Valerian Saliou <valerian@valeriansaliou.name>
// License: Mozilla Public License v2.0 (MPL v2.0)

macro_rules! get_cache_store_client {
    ($pools:expr, $error:expr, $client:ident $code:block) => {{
        // As the DNS server is mono-threaded, it is safe to perform a 'try_get' there, which does \
        //   not wait if no pool is available to serve request answer. This also prevents all \
        //   threads from being blocked in the event of a Redis failure, and thus allow \
        //   Constellation to serve DNS answers from its internal cache.
        let mut last_error = $error;

        for (pool, target) in $pools {
            // Attempt to get the first healthy pool, in order
            match pool.try_get() {
                Some(mut $client) => {
                    debug!("acquired cache store client at: {}", target);

                    // Healthy pool acquired, return immediately (break the acquire loop)
                    return $code;
                }
                None => {
                    warn!("could not acquire cache store client from sub-pool");

                    last_error = $error
                }
            }
        }

        error!("failed getting a cache store client from all pools");

        Err(last_error)
    }};
}